1. Field of the Invention
The present invention relates to an infrared ray detecting apparatus, and more particularly, relates to an improvement of an infrared ray detecting apparatus for measuring a temperature of an object to be measured by detecting an amount of infrared ray radiated from the object.
2. Description of the Prior Art
An infrared ray detecting apparatus is often used as means, for measuring the temperature of an object to be measured, for converting the amount of infrared rays radiated from the object into a quantity of electricity. And, as is well known in the art, the infrared ray detecting apparatus requires an optical chopper. Namely, the optical chopper makes infrared rays to be measured intermittently incident upon an infrared ray detecting element formed by crystals etc., thereby providing thermal pulses in response to the intensity of the infrared rays. Such infrared ray detecting apparatus is mainly used in a microwave oven for cooking food while detecting the temperature of the food.
In Japanese Patent Laying-Open Gazette No. 97612/1980, there is disclosed a microwave oven to which a conventional infrared ray detecting apparatus is applied. With respect to an optical chopper of the infrared ray detecting apparatus as shown in the same, a disc having recesses such as holes is provided in front of an infrared ray detecting element, to be rotated at a constant speed by a motor. Thus, such structure is not suitable for making the detecting apparatus small-sized.
In Japanese Patent Laying-Open Gazette No. 32131/1983, there is disclosed an optical chopper in a new mode which is directed to make an infrared ray detecting apparatus small-sized. In the structure of this chopper, a shutter is vibrated by bimorph elements which are vibrated by electric signals, for intermittently controlling incident infrared rays. Although the bimorph elements are driven by electric signals in the form of sine waves and square waves in such a device, the bimorph elements are preferably driven by square wave signals in view of simplicity of a circuit for generating such electric signals, signal frequencies with respect to temperatures and stability of the amplitude. However, when the bimorph elements are driven by the square waves, the bimorph elements generate abnormal noises sounding click-clack. Such generation of the abnormal noises is caused by abnormal distortion within the bimorph elements, leading to degradation of the bimorph elements and offensiveness to the ear.
In such a device, mounting accuracy of the aforementioned shutter must be considerably improved for performing accurate infrared ray detection, which is extremely difficult.
When the infrared ray detecting apparatus having such bimorph-driven type chopper is applied to an microwave oven, it is difficult to drive the aforementioned bimorph elements at a constant voltage due to change in power supply voltages caused upon on-off operation of a microwave oscillation circuit.